In recent years, model changes at manufacturing sites have been frequently observed in order to realize small lot production in great varieties. In such recent manufacturing sites where cell production has been widely conducted, in order to automate, with use of robots, thread fastening, fitting and attaching components, inserting flexible boards or the like, polishing, etc., such robots are required to be flexibly adaptable to a wide variety of types of components and to various operation steps. Every time components to be handled are replaced, assembling positions, directions, or the like are changed, and the process order of tasks is also changed. Accordingly, the robots need to be adapted to these changes. Those tasks of handling soft articles, such as insertion of a flexible board, are complicated, so that such tasks are still performed manually. A person can perform a complicated task by estimating the degree of warp or the position of such a soft article on the basis of reactive force that can be felt with a hand when the soft article is in contact with a target object and is thus warped.
To the contrary, in a robot, it is impossible to formulate force information or positional information on a soft article that is warped in a different manner or at a different portion in each trial. Therefore, it is quite difficult for such a robot to perform a complicated task in accordance with acquired reactive force. There are strong demands for solving this problem to automate, by means of robots, those tasks that have been primarily performed manually.
In order to realize such demands, there have been conventionally adopted methods of teaching tasks to robots with use of teaching pendants or programming. However, teaching according to these methods needs a quite large number of teaching steps. In addition, it may be impossible in some cases to teach a task that needs complicated movement such as moving a plurality of joints of a robot at one time.
As mentioned above, there are limits in the methods with use of the teaching pendants or programming.
Therefore, conventionally, there has been adopted a method of easily teaching by means of direct teaching, i.e. teaching by touching a robot. The direct teaching has advantages such as enabling intuitive operations, and achieving operations appropriate for physical reactive force because a working person feels the reactive force when the robot is in contact with a target object. On the other hand, in a case where a robot is heavy by itself, the direct teaching also has disadvantages such as that a person cannot support the robot and thus cannot operate the robot, and that the person cannot feel the physical reactive force when the robot is in contact with a target object because of the heavy weight of the robot itself. It is therefore quite important, upon teaching a robot that has poor operability, to improve the operability of the robot.
There has been devised a configuration for direct teaching, in which a distal end of an arm tip of a first robot arm holds a second robot arm that is attached by means of a spring. This configuration including the two robot arms realizes more accurate direct teaching, as compared to the configuration including only one robot arm according to the conventional art (refer to Patent Literature 1).
There has been also adopted a method of displacing a retainer member with small force even in a case of holding a relatively heavy object, by limiting the shift of the retainer member into the horizontal direction and detecting the peripheral environment (the amount of displacement of or force information on a retained target object) to perform impedance control (refer to Patent Literature 2).
On the other hand, in a case where a task of conveying a product or a task of fitting a heavy component is too complicated to realize by means of a robot in a method of using a teaching pendant or programming, such a task has been performed by two working persons. There are strong demands for reducing workloads of working persons in these tasks with use of robots. Upon automation of such a task, it is impossible for a working person to teach the task to a robot by direct teaching because a product is too heavy. In this case, there is adopted a cooperative conveyance method in which the robot and the working person cooperatively convey such a heavy product that is gripped by the robot.
In this cooperative conveyance, there is an idea of causing a robot to generate assistive power, so that the product can be cooperatively conveyed by small operation force. The value of this assistive power is obtained in the following manner. The joint angle of a robot and the position of an arm tip of the robot, as well as force to be applied to a target object by a working person cooperating with the robot are detected respectively, a viscosity coefficient of the fingers of the working person, an elastic modulus thereof, and positions of the fingers at the natural lengths of the working person are estimated respectively from these detected values, and the value of the assistive power is obtained from these estimated values (refer to Patent Literature 3).
There has been also disclosed a configuration for power assistive conveyance upon conveying an object, in which a floating mechanism is provided between a portion gripped by a person and a portion to be conveyed, so that the assistive conveyance is controlled in accordance with the amount of displacement of the floating mechanism (refer to Patent Literature 4).
Citation List
Patent Literature
                Patent Literature 1: JP H04-164584 A        Patent Literature 2: JP 2006-247787 A        Patent Literature 3: JP 2007-76807 A        Patent Literature 4: JP 2005-193340 A        